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Cardiac Out Put

Cardiac Out Put. Lecture by Dr.Mohammed Sharique Ahmed Quadri Assistant professor ,Physiology. Objectives. Define and describe the terms COP, stroke volume, EDV, ESV the ejection fraction. Describe factors affecting cardiac output and venous return.

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Cardiac Out Put

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  1. Cardiac Out Put Lecture by Dr.Mohammed Sharique Ahmed Quadri Assistant professor ,Physiology

  2. Objectives • Define and describe the terms COP, stroke volume, EDV, ESV the ejection fraction. • Describe factors affecting cardiac output and venous return. • Recognize the effect of sympathetic and parasympathetic ANS on heart rate and COP. • Identify Frank starling law. • Understand the principle of measuring the COP (Fick principle, dye dilution method). • Apply the physiological knowledge of factors affecting COP on conditions causing low COP and high COP .

  3. CARDIAC OUTPUT What is Cardiac Output? • It is volume of the blood pumped out by each ventricle per minute .It is about 5 – 5.5 Lit/min • Cardiac Output [COP ] = Heart rate × Stroke volume = 70 beats/min × 70ml/beat = 4900 ml/min ≈ 5liters/min • COP of each ventricle is same.

  4. CARDIAC OUTPUT [COP] • COP increases during exercise, and depending on exercise, it can increase to 20–25 liters/min [up to 35 liters/min is recorded in trained athlete during heavy exercise]. • How ? - By increasing stroke volume and heart rate.

  5. CARDIAC INDEX What is Cardiac Reserve ? • It is the difference between cardiac output at rest and maximum volume of blood that heart can pump per minute. What is Cardiac Index ? • It is cardiac output per minute per square meter of body surface area. • Normal Cardiac Index = 3.2 Liter /min/ sq meter body surface area.

  6. DEFINITIONS WHICH WE WILL USE DURING DISCUSSION OF COP Stroke Volume: It is a volume of blood pumped out by each ventricle per beat. It is about 70 - 80 ml. Stroke volume (SV) = EDV – ESV • End Diastolic Volume: Volume of blood in each ventricle at the end of diastole. It is about 120 – 130 ml. • End Systolic Volume: Volume of blood in each ventricle at the end of Systole. It is about 50 to 60 ml

  7. SV (EDV – ESV) X 100 EDV • Ejection fraction (EF) is the percentage of ventricular end diastolic volume (EDV) which is ejected with each stroke. EF = 75 X 100 = 62.5% 120 Normal ejection fraction is about 50 – 75 %. Ejection fraction is good index of ventricular function.

  8. Factors controlling cardiac out put

  9. Factors controlling cardiac out put • Heart rate : is determined primarily by autonomic influences on SA node • The heart is innervated by both division of autonomic nervous system which can modify the rate as well as strength of contraction. • Parasympathetic innervation through vagus primarily supplies atrium (SA node & AV node) ,parasympathetic innervation of ventricle is sparse. • Cardiac sympathetic innervation supplies both SA node & AV node & also to ventricles.

  10. Factors controlling cardiac out put • Autonomic control of heart rate - + Heart rate Increase Parasympathetic activity Increase sympathetic activity

  11. Factors controlling cardiac out put • Control of heart rate: • Heart rate is determined by balance between Inhibition of SA node by vagus(parasympathetic) & stimulation by sympathetic • Under resting condition parasympathetic discharge dominates • Although heart rate is primarily regulated by autonomic innervation the other factor affect it as well ,the most imp is EPINEPHRINE ,a hormone secreted by adrenal medulla and that act on heart & increases heart rate

  12. Factors controlling cardiac out put • Stroke volume : two types of control influence stroke volume • INTRINSIC CONTROL related to venous return & peripheral resistance • EXTRINSIC CONTROL related to extent of sympathetic stimulation of heart . • Both factors( Intrinsic and Extrinsic ) increase stroke volume by increasing the strength of heart contraction.

  13. Factors controlling cardiac out put • Intrinsic control of stroke volume: • Direct correlation between end diastolic volume & stroke volume • This depends on length tension relationship of cardiac muscle • For cardiac muscle resting cardiac length is less than optimum length at which maximum tension develops • Therefore increasing the increasing the cardiac muscle fiber length closer to optimum length, increases the contractile tension of the heart on the following systole .

  14. Factors controlling cardiac out put • Frank -Starling law of heart: force of contraction is proportional to initial length of cardiac muscle fiber .( intrinsic relation between end diastolic volume and stroke volume) • Greater the diastolic filling larger the end diastolic volume & more the heart is stretched .the more the heart stretched , longer the initial cardiac fiber length before contraction , more will be the force of contraction • EXTENT OF FILLING IS REFFERED TO AS PRELOAD

  15. Factors controlling cardiac out put

  16. Factors Controlling Venous Return

  17. VENOUS RETURN TO THE HEART i).Increased Blood Volume • Veins are capacitance vessels and hold about 60 to 70% of blood, when veins store less blood, more blood is returned to the heart. ii).Skeletal Muscle Pump • Muscle contraction compresses the veins. • This external venous compression decreases venous capacity and increases venous pressure and moves blood towards the heart.

  18. VENOUS RETURN TO THE HEART iii).Respiratory Pump • During respiration(inspiration), intra-thoracic pressure decreases and is less than atmospheric pressure [-5 mmHg]. • This negative chest cavity pressure squeezes blood from the lower veins to the chest, increasing venous returns.

  19. VENOUS RETURN TO THE HEART iv).Increased Sympathetic activity(Vasoconstriction) • Sympathetic Stimulation causes vasoconstriction, which increases venous pressure and drives more blood to right atrium, therefore, more venous returns and increase EDV. v).Cardiac suction effect • Heart plays role in its own filling. During ventricular contraction, AV valves are pulled downward enlarging atrial cavities. • Atrial pressure drops below 0 mmHg and increases venous returns.

  20. VENOUS RETURN TO THE HEART vi).Venous Valves • In the veins, blood can be driven forward only as large veins have one way valve placed at 2 to 4 cm intervals. • These valves prevent back flow of blood that tends to occur when a person stands up.

  21. CARDIAC OUTPUT [COP] • EXTRINSIC CONTROL [factors outside the heart] • Extrinsic control is through sympathetic stimulation. • Sympathetic stimulation and epinephrine increases heart contractility, at any given end – diastolic volume. • Increased contractility results from increased Ca2+ influx triggered by nor- epinephrine and epinephrine.

  22. Effect of Sympathetic stimulation on stroke volume

  23. Factors controlling cardiac out put • Sympathetic stimulation increases the contractility of the heart • Sympathetic stimulation shift the frank starling’s curve to left

  24. Intrinsic & extrinsic control of stroke volume

  25. EJECTION FRACTION • Ejection Fraction is ratio of Stroke Volume to End – Diastolic Volume. EF = [SV ÷ EDV] × 100 • Normal healthy heart has Ejection Fraction of 50 – 75% under resting conditions and may go up to 90% during strenuous exercise. • A failing heart (cardiac failure)  EF maybe 30% or less.

  26. MEASUREMENT OF CARDIAC OUTPUT • Cardiac Output can be measured 1. Fick Principle 2. Dye Dilution Method 3. Doppler Combined with Echocardiography

  27. FICK PRINCIPLE Output of Left Ventricle Oxygen Uptake by lungs ml/min = AO2 - VO2 200 ml / min 200 ml / L – 160 ml / L Art blood – Venous blood [Pul artery] 200 ml/min 40ml / liter = 5 L/min = =

  28. Conditions which alters the cardiac out put • Physiological • Muscular exercise • Emotional states • Posture • Pregnancy

  29. Pathological • Increase in cardiac out put • Hyperthyroidism • Anemia • Fever • Decrease in cardiac out put • Hypothyroidism • Myocardial damage & cardiac failure • Valvular heart diseases • Arrhythmias • Hemorrhage & shock

  30. APPLIED HEART FAILURE What is Heart Failure ? • It is inability of heart to give cardiac output, sufficient to keep pace with body’s demand. • There may be left ventricular failure or right ventricular failure or bi – ventricular failure. • Most common cause heart failure is 1. Heart Attack or Myocardial Infarction 2. Working against Increased after load e.g. hyper tension or aortic valve stenosis

  31. PRE LOAD & AFTER LOAD • PRE LOAD – load on the heart before contraction i.e. end – diastolic volume. • AFTER LOAD – load against which ventricle has to pump i.e. pressure in the artery or arterial blood pressure.

  32. Frank Starling Curve In Heart Failure Cardiac failure

  33. References • Human physiology by Lauralee Sherwood, seventh edition • Text book physiology by Guyton &Hall,11th edition • Text book of physiology by Linda .s contanzo,third edition

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